The present invention relates generally to rotating machinery and more particularly to a torque pin to maintain adjacent disks of a turbine in alignment and to a turbine incorporating the same.
Conventional turbines and compressors (hereinafter referred to collectively as xe2x80x9cturbinesxe2x80x9d) include a rotating shaft supporting a plurality of disks or rings (hereinafter referred to as xe2x80x9cdisksxe2x80x9d). During operation, the shaft and disks are typically rotated at a high speed. To maintain adjacent disks aligned and inhibit relative movement between the disks as the disks are rotated, torque pins are employed to engage each pair of adjacent disks at circumferentially spaced locations. In large turbines, hundreds of torque pins are used. The design of the torque pins therefore, has a significant impact on the manpower required during installation and maintenance of large turbines.
Different types of torque pins to align adjacent disks and inhibit relative movement between adjacent disks have been considered. For example, one common type of torque pin includes an elongate body having flanges at its opposite ends. Each flange is bolted to a respective one of a pair of adjacent disks. Although this type of torque pin works satisfactorily to align adjacent disks, the design suffers a serious drawback. Since this type of torque pin must be bolted to adjacent disks, installation and removal of the torque pin is extremely time consuming.
To facilitate installation, Westinghouse Canada Inc. manufactures an alternative torque pin design. This torque pin includes an elongate cylindrical body having a cam slot formed in the sidewall of the body. A centrally disposed, threaded bore extends from one end of the body to the cam slot. A cam is accommodated in the cam slot and is rotatably coupled to the body. The cam can be moved from a retracted position within the body, to an extended position where the cam extends outwardly of the body. When the cam extends outwardly of the body, the cam engages adjacent disks to maintain them in alignment. During installation, a key is used to hold the torque pin in place between adjacent disks. A threaded fastener is then advanced into the bore until the fastener bears against the cam and forces the cam out of the cam slot to the extended position. The threaded fastener is advanced down the bore to the point where the fastener splits. In this manner, the fastener cannot be unthreaded from the bore. As a result, the cam is unable to move back into the body and therefore, remains in the extended position.
Although this torque pin design requires less time to install than the previously described torque pin, it is still relatively time consuming to install. Also, if the fastener does not split properly, during operation of the turbine, vibrations may cause the fastener to dislodge from the bore, in which case, the cam is then able to rotate back into the body. If this occurs, the torque pin may dislodge from between adjacent disks, which can be catastrophic. In addition, since the fastener splits within the bore when the torque pin is properly installed, the torque pin cannot be re-used once it has been removed during maintenance of the turbine.
As will be appreciated, improvements in the design of torque pins are desired. It is therefore an object of the present invention to provide a novel torque pin and to a turbine incorporating the same.
According to one aspect of the present invention there is provided a torque pin to maintain rotating disks in alignment comprising:
an elongate body having a slot provided in a sidewall thereof;
a locking element coupled to said body and being moveable relative to said body from a retracted condition where said locking element is accommodated in said slot to an extended condition where said locking element extends outwardly beyond said sidewall; and
a retaining mechanism disposed in said body, said retaining mechanism being biased towards said slot to maintain said locking element in said extended condition.
In a preferred embodiment, the retaining mechanism maintains the locking element in the extended condition and in the retracted condition. In the extended condition, the retaining mechanism extends into the slot to inhibit the locking element from moving to the retracted condition. In the retracted condition, the retaining mechanism abuts the locking element to inhibit the locking element from moving to the extended condition. Preferably, the retaining mechanism includes a spring and a retaining element. The spring urges the retaining element into contact with the locking element when the locking element is in the retracted condition and urges the retaining element into the slot when the locking element is in the extended condition.
In one embodiment, the body has a centrally disposed bore therein with the bore including a larger diameter portion and a smaller diameter portion to define an internal shoulder. The larger diameter portion intersects the slot. The retaining element includes a smaller diameter portion and a larger diameter portion to define an annular abutment surface. The spring is disposed in the larger diameter portion of the bore and bears against the larger diameter portion of the retaining element. The annular abutment surface contacts locking element in the retracted condition and contacts the internal shoulder in the extended condition so as to position the larger diameter portion in the slot. Preferably, the smaller diameter portion of the bore extends to the end of the body with the smaller diameter portion of the bore and the smaller diameter portion of the retaining element being generally the same length.
According to another aspect of the present invention there is provided a torque pin comprising:
a generally cylindrical body defining an external sidewall and having a longitudinally extending bore formed therein, said body also having a radially extending slot provided in said sidewall that intersects said bore;
a cam pivotally coupled to said body and being accommodated by said slot, said cam being moveable between an unlocking condition where said cam is fully accommodated by said slot and a locking condition where said cam is partially accommodated by said slot and extends outwardly beyond said sidewall; and
a retaining mechanism disposed in said bore, said retaining mechanism acting on said cam when said cam is in said unlocking condition and moving into said slot when said cam is in said locking condition thereby to inhibit said cam from returning to said unlocking condition.
According to yet another aspect of the present invention there is provided a turbine comprising:
a rotatable shaft;
a plurality of disks on said shaft, adjacent disks having facing recesses formed therein to define torque pin cavities; and
torque pins accommodated in said torque pin cavities, each of said torque pins including:
an elongate body having a slot provided in a sidewall thereof;
a locking element coupled to said body and being moveable relative to said body between a retracted condition where said locking element is accommodated in said slot and an extended condition where said locking element extends outwardly beyond said sidewall; and
a retaining mechanism disposed in said body, said retaining mechanism being biased towards said slot to maintain said locking element in said extended condition.
The present invention provides advantages in that the torque pin can be installed and removed easily and quickly by a single technician thereby significantly reducing the manpower required during installation and maintenance of large turbines. Also, since the torque pin body fully captures the retaining element, the torque pin is unlikely to be dislodged during operation of the turbine. Furthermore, the centrifical forces placed on the torque pin due to the high speeds of rotation of the turbine, enhance the performance and security of the torque pin.